Top 5 Unsolved Brain Mysteries

"Sweet dreams are made of this," sang Annie Lennox during her stint in the Eurythmics in the 1980s. But you might notice that Lennox is suitably vague about what exactly "this" is. And really, no one knows what sweet dreams are made of, why we have them or even what we're doing sleeping our life away anyway.

Can you believe that? Every night we carve out a few hours of shut-eye, and scientists don't even know why! They do know that it's extremely damaging if a person doesn't get enough sleep, and it's possible that sleep once served some sort of evolutionary benefit. Sleep would be an extremely beneficial distraction if early man had wanted to take a midnight stroll at the time when saber-tooth tigers were on the prowl [source: BBC]. On the other hand, it's not a particularly advantageous trait to carry forward in this age of electricity as the process takes up a lot of time (about a third of our life) and renders the dreamer defenseless against predators [source: Eagleman].

There are a few theories as to why we need so much sleep. One idea is that sleep is restorative to the body, giving it an opportunity to rest. But if rest is the goal, why does our brain remain hard at work? It's possible that while we sleep, the brain is practicing and running problem-solving drills before completing actions in the real world. There are several studies that show that learning can't take place without sleep to reinforce the knowledge [source: Schaffer].

Some of these studies may have real implications for students. One researcher claims that it would be better for students to review information until they were tired, then slept, as opposed to pulling an all-nighter [source: BBC]. Some schools have changed the time of that first bell so that middle and high school students can get a little more snooze time [source: Boyce, Brink].

So let's say these students actually go to sleep, as opposed to engaging in more nefarious behaviors. What happens then? When the dreaming state of REM sleep was discovered in 1951, it was described as a "new continent in the brain" [source: Schaffer]. Though scientists have tried to make inroads on this uncharted continent, mysteries remain about its topography. Like sleep, dreaming may represent some sort of personal gym time for the brain, with dreams allowing a person to work out emotional issues and solidify thoughts and memories.

Or, it's possible that life is but a dream, as the song "Row, Row, Row Your Boat" taught us. When you're asleep, you're experiencing a ton of visual stimuli that the brain is somehow processing. In an awake state, there may be additional stimuli for different senses, but the brain may be doing the same thing with them. If the brain works just as hard sleeping as it is when we're awake, then maybe life is a waking dream [source: Eagleman].

Let's row our boat over to the next page and investigate the mysterious case of human memory.